1. Field of Invention
The invention relates to a light-emitting diode (LED) device and a manufacturing method thereof.
2. Related Art
A light-emitting diode (LED) device is a lighting device made of semiconductor materials. The LED device has the advantages of small size, low power consumption, no radiation, mercury-free, long lifetime, fast response speed and high reliability. With the continuous progress of the recent technology, the application range thereof covers the information, communication, customer electronics, vehicle, lighting and traffic sign.
With reference to FIG. 1, a conventional LED device 1 includes a substrate 11, an epitaxial layer 12, a buffer layer 14, an N-type electrode 16, a P-type electrode 17 and a transparent conductive layer 18. The buffer layer 14, epitaxial layer 12 and transparent conductive layer 18 are disposed on the substrate 11 in sequence.
The epitaxial layer 12 includes an N-type semiconductor layer 121, a light-emitting layer 122 and a P-type semiconductor layer 123 in sequence. The N-type semiconductor layer 121 is disposed on the buffer layer 14. The light-emitting layer 122 is disposed on the N-type semiconductor layer 121. The P-type semiconductor layer 123 is disposed on the light-emitting layer 122. The N-type electrode 16 is electrically connected to the transparent conductive layer 18 via the epitaxial layer 12, and the P-type electrode 17 are electrically connected to the transparent conductive layer 18.
In general, the voltage and current of the LED device 1 usually have an exponential relationship. When the N-type electrode 16 and the P-type electrode 17 are applied with a voltage larger than the threshold voltage, the current through the LED device 1 is increased sharply. At the same time, the LED device 1 starts to light.
However, in the conventional structure of the LED device 1, the current distribution is non-uniform and is concentrated in the area A. This will cause the exceed current density in local area, which affects the lighting efficiency and results in overheat of the local area. Moreover, the lifetime of the LED device 1 will be shortened.